The present invention relates to isocyanate-derived foams and to a precursor composition useful in their preparation, more particularly, to polyurethane and urethane-modified, polyisocyanurate foams and to a precursor useful in the preparation of said foams.
Due to their desirable physical properties such as dimensional stability, compressive strength, thermal conductivity and the like, isocyanate-derived foams are employed in a wide variety of applications including insulation, structural reinforcement and electrical encapsulation. In addition to the aforementioned properties, for use in various applications, the foams must also advantageously exhibit some degree of fire resistance.
A foam exhibiting comparatively excellent fire-resistant properties is obtained by the trimerization reaction of an isocyanate to form an isocyanurate. However, the resulting, unmodified polyisocyanurate foams are extremely friable (weak) materials which have a tendency to crumble or to be reduced to a powder. In addition, when subjected to elevated temperatures, the unmodified polyisocyanurate foams are liable to form cracks. These cracks form bridges across which occurs a breakdown of the otherwise high insulating properties of the foam.
To reduce the friability of an unmodified polyisocyanurate foam, it has heretofore been common to employ relatively small amounts of an active hydrogen-containing compound per each equivalent of isocyanate to make a urethane-modified, isocyanurate foam. See, for example, U.S. Pat. Nos. 3,940,517; 3,922,238 and 4,204,019. Unfortunately, elevated temperatures are often required to initiate the reaction of the isocyanate in the formation of the disclosed foams. This necessitates the energy consuming and otherwise undesirable step of heating the reaction mixtures prior to foam formation which often results in processing problems and/or non-uniformity in the resulting foam. In addition, a number of the known urethane-modified isocyanurate foams can only be prepared using a prepolymer of the reaction product of an isocyanate with a polyol as one of the reactants. Moreover, further increases in the strength of the foams are still required.
In view of the aforementioned deficiencies in the prior art, it remains highly desirable to provide an isocyanate-derived foam having desirable physical properties, including fire-resistant properties, which foam can readily be prepared from a reaction mixture having desired processability characteristics.